Many different physical ideas can describe the
same physical reality. Thus, classical electrodynamics can
be described by a field view, or an action at a distance view,
etc. Originally, Maxwell filled space with idler wheels, and
Faraday with fields lines, but somehow the Maxwell equations
themselves are pristine and independent of the elaboration of
words attempting a physical description. The only true physical
description is that describing the experimental meaning of the
quantities in the equation - or better, the way the equations are
to be used in describing experimental observations. This being the
case perhaps the best way to proceed is to try to guess equations,
and disregard physical models or descriptions. For example,
McCullough guessed the correct equations for light propagation in
a crystal long before his colleagues using elastic models could
make head or tail of the phenomena, or again, Dirac obtained his
equation for the description of the electron by an almost purely
mathematical proposition. A simple physical view by which all the
contents of this equation can be seen is still lacking.

Therefore, I think equation guessing might be the best method to
proceed to obtain the laws for the part of physics which is
presently unknown. Yet, when I was much younger, I tried this
equation guessing and I have seen many students try this, but it
is very easy to go off in wildly incorrect and impossible
directions. I think the problem is not to find
the best or most efficient method to proceed to a discovery, but
to find any method at all. Physical reasoning does help
some people to generate suggestions as to how the unknown may be
related to the known. Theories of the known, which are described
by different physical ideas may be equivalent in all their
predictions and are hence scientifically
indistinguishable. However, they are not psychologically identical
when trying to move from that base into the unknown. For different
views suggest different kinds of modifications which might be made
and hence are not equivalent in the hypotheses one generates from
them in ones attempt to understand what is not yet understood. I,
therefore, think that a good theoretical physicist today might
find it useful to have a wide range of physical viewp\oints and
mathematical expressions of the same theory (for example, of
quantum electrodynamics) available to him. This may be asking too
much of one man. Then new students should as a class have
this. If every individual student follows the
same current fashion in expressing and thinking about
electrodynamics or field theory, then the variety of hypotheses
being generated to understand strong interactions, say, is
limited. Perhaps rightly so, for possibly the chance is high that
the truth lies in the fashionable direction. But, on the
off-chance that it is in another direction - a direction obvious
from an unfashionable view of field theory - who will find it?
Only someone who has sacrificed himself by teaching himself
quantum electrodynamics from a peculiar and unusual p\oint of
view; one that he may have to invent for himself. I say
sacrificed himself because he most likely will get nothing from
it, because the truth may lie in another direction, perhaps even
the fashionable one.

But, if my own experience is any guide,
the sacrifice is really not great because if
the peculiar viewp\oint taken is truly experimentally equivalent
to the usual in the realm of the known there is always a range of
applications and problems in this realm for which the special
viewpoint gives one a special power and clarity of thought, which
is valuable in itself. Furthermore, in the search for new laws,
you always have the psychological excitement of feeling that
possibly nobody has yet thought of the crazy possibility you are
looking at right now.